John Snow was a well-known doctor   in London in the 19^th century. He wanted to find the c【小题1】 of cholera in order to control it. In 1854 when a cholera 【小题2】 out, he began to gather information. He marked on a map where all the dead people had lived and he found that many people who had 【小题3】 the dirty water from the 【小题4】 died. So he decided that the polluted water carried cholera. He suggested that the source of all water supply be examined and new methods of dealing with polluted water be found. Finally, “King Cholera” was【小题5】.

In general, doctors in those days had two【小题1】 theories to explain how cholera spread. One theory was that bad air caused the disease. The other was that cholera was caused by an【小题2】 from germs in food or water. Snow【小题3】 to the second theory.